This invention relates to dielectric ceramics, and more specifically to ferroelectric ceramics composed principally of barium titanate (BaTiO.sub.3) for use in capacitors, among other applications.
BaTiO.sub.3 is a well known major component of ferroelectric ceramics. The ceramics have also been known wherein each crystal grain is constituted of a ferroelectric core and a paraelectric shell, with the former nested in the latter, with a view to a higher dielectric constant and a more favorable temperature characteristic (change in capacitance with temperature). Magnesium (Mg) is employed, usually in combination with other additives, to create the paraelectric shells by dispersion in the ferroelectric crystal grains.
An objection to the prior art BaTiO.sub.3 --Mg ceramics of the core-shell crystal grain configuration concerns the depth of the Mg shells. As far as the applicant is aware, no particular measure has been taken in the ceramics industry to preclude the dispersion of Mg particles too deep into the BaTiO.sub.3 crystal grains. The shells of the resulting ceramics have therefore been not so thin as could be desired, failing to provide ceramics that were sufficiently high in dielectric constant and favorable in temperature characteristic.
A current trend in laminated ceramic capacitors is toward larger capacitances, with, however, the dielectric layers made thinner. Moreover, very high standards of quality are required for such capacitors. As so far manufactured, the BaTiO.sub.3 --Mg ceramics have become totally incapable of providing capacitors meeting such standards.